Evaluation of “Dream Herb,” Calea Zacatechichi, for Nephrotoxicity
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Hindawi Publishing Corporation Journal of Toxicology Volume 2016, Article ID 9794570, 7 pages http://dx.doi.org/10.1155/2016/9794570 Research Article Evaluation of (Dream Herb,) Calea zacatechichi,for Nephrotoxicity Using Human Kidney Proximal Tubule Cells Miriam E. Mossoba, Thomas J. Flynn, Sanah Vohra, Paddy Wiesenfeld, and Robert L. Sprando Center for Food Safety and Applied Nutrition (CFSAN), Office of Applied Research and Safety Assessment (OARSA), Division of Toxicology (DOT), US Food and Drug Administration (US FDA), Neurotoxicology and In Vitro Toxicology Branch (NIVTB), 8301 Muirkirk Road, Laurel, MD 20708, USA Correspondence should be addressed to Miriam E. Mossoba; [email protected] Received 29 February 2016; Accepted 1 August 2016 Academic Editor: Orish Ebere Orisakwe Copyright © 2016 Miriam E. Mossoba et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A recent surge in the use of dietary supplements, including herbal remedies, necessitates investigations into their safety profiles. “Dream herb,” Calea zacatechichi, has long been used in traditional folk medicine for a variety of purposes and is currently being marketed in the US for medicinal purposes, including diabetes treatment. Despite the inherent vulnerability of the renal system to xenobiotic toxicity, there is a lack of safety studies on the nephrotoxic potential of this herb. Additionally, the high frequency of diabetes-associated kidney disease makes safety screening of C. zacatechichi forsafetyespeciallyimportant.Weexposedhuman proximal tubule HK-2 cells to increasing doses of this herb alongside known toxicant and protectant control compounds to examine potential toxicity effects of C. zacatechichi relative to control compounds. We evaluated both cellular and mitochondrial functional changes related to toxicity of this dietary supplement and found that even at low doses evidence of cellular toxicity was significant. Moreover, these findings correlated with significantly elevated levels of nephrotoxicity biomarkers, lending further support forthe need to further scrutinize the safety of this herbal dietary supplement. 1. Introduction expression [11–13]. In addition, germacrolides are part of the class of sesquiterpene lactones, which can also exhibit Calea zacatechichi (also called Calea ternifolia or “Dream negative effects on both prokaryotic and mammalian cells Herb”) is a flowering plant native to Central America and [14]. The cytotoxicity of both flavonoids and sesquiterpene has a long tradition of use as a medicinal plant in indige- lactones has been exploited for use as therapy against cancer nous cultures [1]. Exposure through inhalation (smoking) or [15, 16]. ingestion (as tea) is primarily used to temporarily intensify Despite clear evidence that at least some of the biologi- lucid dreaming. It is also widely consumed to treat problems cally active components of C. zacatechichi have the potential associated with the gastrointestinal and endocrine systems to be cytotoxic, safety evaluations of whole forms of this [2]. It has recently been marketed as a dietary supplement herbal supplement are lacking, especially ones that focus on in the management of diabetes due to its ability to induce the kidney. The kidneys use a complex transport system to hypoglycemic effects [3–5] although its mechanism(s) of eliminate unwanted chemicals, regulate blood pressure and action remain unclear. glucose levels, and maintain a balanced pH [17]. However, as The oneirogenic and other biological effects of C. zacat- the glomerular filtrate passes through the tubular system, the echichi are attributed in part to their flavones and germa- reabsorption of water and electrolytes by the proximal tubule crolides components [6–10]. However, flavones represent a cells can progressively concentrate chemicals in the lumen class of flavonoids that have been shown to carry cytotoxic that do not get reabsorbed. Unfortunately, the proximal effects in part through induction of cytochrome P450 enzyme tubules can become exposed to toxic concentrations of such 2 Journal of Toxicology chemicals, even when blood concentrations are relatively processes. Treated cells in black-wall, clear bottom 96-well lower, leaving the kidneys vulnerable to injury [17]. In the plates were equilibrated to room temperature for 30 minutes, case of C. zacatechichi,itisunknownwhetheranyofits during which time water in the outer wells was replaced with componentscanbenephrotoxic,butgiventhatitismarketed approximately 100 uL of treatment or media only controls. to diabetics, any preexisting diabetic nephropathy marked Following that, an equal volume of CellTiter-Glo working by glomerular or proximal tubule damage [18–20] could solution was added to each well. Plates were placed on induce further kidney damage. Therefore, we focused our an orbital shaker for 2 minutes to induce cell lysis and research on screening for the potential nephrotoxicity of then incubated for an additional 10 minutes before being C. zacatechichi using an in vitro model of human proximal read on an OMG Fluorostar plate reader (BMG LABTECH, tubule cells. We chose the HK-2 cell line as our human Ortenberg, Germany) to measure the levels of luminescence proximal tubule model for its robust performance in many emitted from each well. in vitro toxicology studies [21–25]. We compared the effects of exposing HK-2 cells to C. zacatechichi and two control 2.4. Reactive Oxygen Species Assay. Quantification of reactive compounds, a known renal toxicant (cisplatin) and a known oxygen species (ROS) was determined using Promega’s ROS- renal protectant (valproic acid), and evaluated their dose- Glo H2O2 luminescence-based detection system and data dependent effects on cytotoxicity, mitochondrial injury, and were normalized to cell viability. Following 24 hrs of direct four kidney-specific biomarkers of toxicity [26–28]: (1) Kid- exposure to C. zacatechichi, cells were incubated with H2O2 ney Injury Molecule-1 (KIM-1), (2) Albumin, (3) Cystatin substrate and detection reagent, as recommended in the C, and (4) 2-microglobulin (B2M). KIM-1 is expressed manufacturer’s instructions. Luminescence was read on an in tubular epithelial cells in response to injury. Albumin, OMG Fluorostar plate reader. Cystatin C, and B2M are indicators of impaired reabsorption by the proximal tubules. In this study, we demonstrate that 2.5. Mitochondrial Membrane Potential Assay. Changes in C. zacatechichi is capable of inducing both cellular and mitochondrial membrane potential (MMP) were evaluated organellar toxicity in proximal tubule cells. using the ratiometric dye JC-10 (Enzo, Farmingdale, NY). HK-2 cells that were directly exposed to C. zacatechichi were 2. Materials and Methods stained with 20 uM JC-10 (final concentration) for 2 hours, washed, and then read by plate reader (OMG Fluorostar). 2.1. Characterization of Calea zacatechichi Extract. Voucher Excitation was set at 485 nm and emission at 520 and 590 nm samples of C. zacatechichi deposited at the University of was measured. We also verified that extract or media alone Mississippi, National Center for Natural Products Research did not produce significant emission signals. (NCNPR) (NCNPR #2443), were authenticated using macroscopy and microscopy methods by an NCNPR 2.6. Nephrotoxicity Biomarker Assays. Culture supernatants botanist. A methanol-extract of C. zacatechichi was provided from cells treated for 24 hours with C. zacatechichi,cisplatin, in lyophilized form by NCNPR and was stored in the dark at ∘ andvalproicacidatdosesof333and111g/mL were evaluated 4 C in a vacuum chamber. Dried extract of C. zacatechichi forlevelsofbiomarkersofkidneytoxicity:KidneyInjury- was analyzed by LC/QTof as described previously [29]. 1 (KIM-1), Albumin, Cystatin C, and beta-2-microglobulin Compounds were putatively identified by matching exact (B2M) using the Human Kidney Toxicity kits (Bio-Rad, mass of analytes with components of C. zacatechichi reported Hercules, CA). Following the manufacturer’s protocol, plates in the literature [8, 30–33]. wereblocked,washed,andincubatedwithsamples,standard solutions detection antibodies, before being given a final 2.2. Cell Culture and Treatments. HK-2 cells were grown, wash. Plates were read using a Luminex 200 instrument (Bio- maintained, and treated in a manner similar to that described Rad). Biomarker expression levels were normalized to cell previously [29]. Stock treatment solutions of C. zacatechichi, viability. nephrotoxicant (positive control) cis-diamineplatinum(II) dichloride (cisplatin) (Sigma-Aldrich, St. Louis, MO), and 2.7. Statistics. Microsoft Excel and Prism (GraphPad, San nephroprotectant (negative control) valproic acid (Sigma- Diego, CA) were used for calculations and analyses of all Aldrich) were made by weighing out their powders, dissolv- data collected. Student’s -tests or 2-way ANOVAs were used ing them in DMSO, and diluting this mixture with media to determine whether dose-matched treatment effects were for a final DMSO stock solution of 0.4% or less. Cells were statistically significant at values less than 0.01 or 0.001 as incubated overnight and treated in triplicate for 24 hours at indicated. the dose range of 0–1000 g/mL. 3. Results 2.3. Cytotoxicity Assay. Treatment-related cytotoxicity was determined using the established CellTiter-Glo Cell Viability 3.1. Characterization